External hardware (also called peripherals) refers to every device that connects to a computer from the outside — through a port, cable, or wireless link — rather than sitting on the motherboard inside the case. The system unit itself contains internal hardware: processor, memory, storage, and the mainboard. Anything you plug into that system unit, from a keyboard to a barcode scanner to an industrial sensor, is external hardware. External devices exist to get data in, get results out, store information, or connect the machine to a network.
External hardware is usually grouped by function. Input devices include keyboards, mice, barcode scanners, RFID readers, cameras, microphones, and touchscreens. Output devices include monitors, projectors, printers, label printers, speakers, and indicator lamps. Some devices do both — a touchscreen monitor or a USB headset is input and output at once. Storage peripherals cover USB flash drives, external SSD and HDD enclosures, and SD cards. Networking hardware covers Ethernet switches, Wi-Fi adapters, and cellular modems, while power hardware covers AC-DC adapters, UPS units, and DC input jacks.
The connection point matters as much as the device. Each external device needs a matching port, enough bandwidth, and often enough power from the host. The table below maps common interfaces to the hardware typically attached to them.
| Interface | Typical
